The present invention relates to a duplicator in a magnetic bubble memory with non-implanted patterns and to a process for producing such a duplicator. It also relates to a magnetic bubble memory having at least one duplicator according to the invention.
The invention more particularly applies to the storage of binary information or bits, materialized in the form of separate magnetic domains called bubbles. These generally cylindrical domains have a magnetization which is the reverse of that of the remainder of the magnetic material (garnet) in which said domains are formed. In this memory, the duplication of the magnetic bubbles makes it possible to carry out duplication by individual bits or by bit blocks.
In a monocrystalline magnetic layer, such as a magnetic garnet film, supported by an amagnetic monocrystalline garnet, the domains or magnetic bubbles are stably formed by the application of a d.c. magnetic field Hp perpendicular to the plane of the magnetic layer. In practice, this magnetic field is produced by a permanent magnet, thus ensuring the non-volatility of the information contained in the memory.
In a magnetic bubble memory, the displacement of the bubbles is brought about by applying a rotary d.c. field H.sub.T in a direction parallel to the magnetic layer surface. The bubbles are displaced around so-called propagation patterns, defined in the upper part of the magnetic layer.
These patterns, which are in the form of disks, lozenges, triangles, T's, etc, can be made from a material based on iron and nickel, or can be obtained by implanting ions in the upper part of the magnetic layer, through a mask making it possible to define the shape of these patterns. In the latter case, in view of the fact that ion implantation only takes place around the patterns, the latter are called non-implanted patterns. The propagation patterns are generally contiguous and as a result of their shape, two adjacent patterns define two cavities or hollows between them.
The displacement of the bubbles along said patterns generally takes place during a period equal to one third of the rotation cycle of the planar magnetic field H.sub.T, the bubbles remaining stationary in the cavities defined between two adjacent patterns throughout the remainder of the cycle. These cavities constitute so-called stable positions. Shift registers are formed, in which the bit 1 is represented by the presence of a bubble and the bit 0 by the absence of a bubble.
In addition to these propagation patterns, it is necessary to use electrical conductors for carrying out writing, information logging, non-destructive reading, register-to-register transfer and erase functions in the bubble memory.
One of the main types of known bubble memories comprises a system of so-called loops or registers used for the storage of information, associated with one or two so-called major loops or registers constituting the access stations to the memory. The minor loops are adjacently longitudinally arranged, whilst the major loops are oriented perpendicularly to the minor loops. The magnetic bubbles are located in the minor loops and can be transferred to the major loops and vice versa, by means of unidirectional or bidirectional transfer gates or ports.
When a single major loop is used, the reading and writing of information takes place by means of said single loop. In the first case, reference is made to a memory having a major-minor organization. However, when two major loops are used, the writing of information takes place by means of one of these two loops and the reading of the information by means of the other loop. These major loops are generally located on either side of minor loops. In the latter case (two loops), reference is generally made to a memory having a serial-parallel.
In the aforementioned bubble memories, the production of a bubble on a major loop, corresponding to the writing of an information bit is carried out by applying a high current to a generally U-shaped conductor, which passes through the propagation patterns forming the major loops. This operation, which is generally known as nucleation, is carried out when the bubble is in a cavity defined between two adjacent patterns.
Following nucleation, the bubble is propagated, by the application of the rotary field H.sub.T, to the major loop, to the transfer gate, in order to transfer the bubble from the major loop to a minor loop. These transfer gates are generally constituted by a U-shaped conductor passing through the patterns forming the minor loop. The application of a current pulse to said conductor makes it possible to extend each bubble between the tops of the propagation patterns of the major loops and those corresponding to the minor loop and then, the stopping of the current pulse leads to the contraction of the bubbles on the minor loop. Transfer is then completed. Thus, the information is stored on the minor loop.
The reading of this information takes place by transferring a magnetic bubble from a minor loop to a major loop, said reading being destructive. The magnetic bubble is transferred to a detection path of the major loop, so that it can be destructively detected by a magnetoresistive detector, generally based on iron and nickel. In order not to lose the information during reading, it is necessary to duplicate the magnetic bubble. The daughter bubble can then be transferred to the magnetoresistive detector and the mother bubble will be reinjected into the site occupied by the original bubble in the minor loop.
A duplication method was described in U.S. Pat. No. 4,253,159, filed on Dec. 3, 1979 and entitled "Ion implanted bubble memory with replicate port". This patent uses a single major loop and non-implanted propagation patterns.
According to this patent, a magnetic bubble is transferred from a minor loop to the major loop. Duplication then takes place on the major loop by means of a conductor passing through it, to which is applied a current pulse. This leads to the elongation of the bubble on either side of the two parallel propagation paths formed by the two sides of the major loop, followed by the splitting of said bubble into two. One of these bubbles is then transferred on a detection path to the magnetoresistive detector and the other bubble is reinjected into the minor loop at the site occupied by the original bubble.
A magnetic bubble memory having as the propagation pattern non-implanted patterns and having a structure and operation such as described in the aforementioned U.S. Patent only makes it possible to carry out a duplication of the bubbles corresponding to a bit-by-bit duplication. These memories do not permit the duplication of a group or block of bits.
This reading method has at least two disadvantages. The first disadvantage results from the fact that the reading of an information bit requires, apart from the duplication of the bubble to be read, the transfer of said bubble from the minor loop to the major loop and then the reinjection, following duplication, of said bubble into the minor loop at the site which was previously occupied. Moreover, in order that duplication can take place correctly, it is necessary for the current pulse to be applied to the extension conductor at a very precise time with respect to the phase of the rotary field H.sub.T. The phase margin on this current pulse is very small.
Another duplicator construction is known, which utilizes the same duplication method. A bubble to be duplicated is firstly transferred from a minor loop to the major loop and is then duplicated between the major loop and another propagation path. This duplication is carried out by two conductors, namely an extension conductor positioned between the major loop and the other propagation path and a current conductor perpendicular to the extension conductor. The bubble remaining on the major loop is supplied to the detector and the bubble produced by duplication on the other propagation path is returned to the minor loop.
As in the aforementioned U.S. patent, this duplication method does not appear to simply permit the duplication of bit blocks between minor loops and the major reading loop. Moreover, the phase margin between the extension and breaking current pulses and the rotary field H.sub.T remains very small, approximately 90 ns, which makes said duplication difficult in practice.
Magnetic bubble memories with non-implanted patterns are also known, whose structure permits a duplication of bit blocks.
The article "Design and characteristics of 4 .mu.m period ion-implanted bubble devices with major line block replicate gate" published in IEEE TRANSACTIONS ON MAGNETICS, Vol. MAG-19, No. 5, September 1983, describes such a non-implanted pattern memory, in which iron-nickel patterns are positioned between each minor loop and a major loop. Reading takes place in three stages:
transfer of the bubble on the minor loop to another iron-nickel pattern, PA1 duplication by applying a current pulse to a conductor covering the iron-nickel pattern, PA1 transfer of a bubble to the major loop and reinjection of the other bubble into the minor loop. PA1 a plurality of first groups of non-implanted patterns, called minor loops, which are aligned along a planar crystallographic axis for the easy magnetization of the magnetic material, PA1 a second group of non-implanted patterns, called the major writing loop, arranged perpendicularly to the minor loops, PA1 means for generating bubbles on the writing loop, PA1 means for the block transfer of a bit from the writing loop into each minor loop, PA1 a third group of non-implanted patterns, called the major reading loop, arranged perpendicular to the minor loops, PA1 means for detecting bubbles on the reading loop, PA1 and a duplication means according to the invention for the blockwise duplication of a bit of each minor loop in the reading loop.
A memory having the structure and function of the types described in this article suffers from the disadvantage of requiring a double transfer of the bubble to be read. To this must be added the complexity of the construction of the memory, which has non-implanted patterns and iron-nickel patterns.
The article "Design of a block replicate gate for ion-implanted bubble devices" published in IEEE TRANSACTIONS ON MAGNETICS, Vol. MAG-18, No. 6, November 1982, describes a bubble memory in which a bubble to be read is directly duplicated without it being necessary to transfer it before and after duplication. An extension conductor is arranged along the minor loop axis, between the end of the minor loop and a stable position of the major loop. A breaking means is also arranged perpendicularly to the conductor between the minor loop and the major loop. This breaking means comprises either a paramagnetic bar formed by locally making the material amorphous by high ion implantation, or by a non-implanted pattern. FIG. 1 is a diagram illustrating duplication in a bubble memory with non-implanted patterns in accordance with said method.
FIG. 1 shows a minor loop 2, a major loop 4, an extension conductor 6 and a breaking means 7. The minor loop 2 comprises a succession on non-implanted patterns 10, which are aligned along an easy magnetization axis 112. The major loop 4 comprises non-implanted patterns 10 of an identical nature and aligned in a direction perpendicular to the axis of the minor loop 2. These non-implanted patterns are produced in a layer of magnetic material. The extension conductor 6 is then produced above said layer.
This extension conductor 6 is generally U-shaped and is centered on the axis of the minor loop 2. The base of extension conductor 6 is located in the vicinity of the end of the minor loop 2 and extends up to the major loop 4. The breaking means 7 is either a rectangle or a V-shape, and is centered on the axis of the extension conductor 6.
A bubble of the minor loop 2 is duplicated by applying a pulse to extension conductor 6, when said bubble is at the end of the minor loop 2 at the base of conductor 6. This current pulse extends the bubble up to the major loop 4. The breaking of this bubble is sided by the breaking means 7, whose presence produces a magnetic field. Thus, the bubble on the minor loop is duplicated without it being necessary to transfer it.
However, it is necessary to apply a contraction pulse to the extension conductor 6, when the bubble is extended in order that breaking or splitting takes place. The duration of this pulse must be less than approximately 50 ns to prevent the destruction of the bubbles. From the electronic standpoint it is difficult to achieve this short duration.
The displacement of the bubble with the rotary field will now be described with reference to FIGS. 2a to 2d in which the extension conductor is not shown. Each of these drawings show corresponding minor and major loops, as well as the phase of the rotary field H.sub.T, indicated by an arrow.
In FIG. 2a, bubble 12 is substantially at the end of the minor loop 2. In FIG. 2b, it has reached said end and is expanded by applying a current pulse to the extension conductor. The presence of the breaking means aids the breaking or splitting of the bubble and, as a result of a contraction pulse in the extension conductor, the bubble is finally duplicated. FIGS. 2c and 2d illustrate the movement of the original bubble 12 on minor loop 2 and of the duplicated bubble 14 on the major loop 4.
It is known that the stable positions of the bubble, i.e. the positions in which the bubble can remain stationary for a large part (e.g. exceeding T/2) of the period T of the rotary field H.sub.T, are constituted by cavities located at the junction of two consecutive non-implanted patterns. Between two successive cavities, the bubble is continuously displaced under the action of the rotary field H.sub.T. The bubble 12 of the minor loop 2 is thus in a non-stable position, when expanded and broken or split in the manner shown in FIG. 2b. The extension and contraction current pulses must consequently be very short and very well synchronized in order that duplication takes place correctly. The phase error on these two pulses with respect to the rotary field H.sub.T is consequently very small.